1. Field of the Invention
The present invention relates to a probe and a contour measuring instrument. For example, the present invention relates to a contour measuring instrument and a probe used when a contour such as a profile and roughness of a surface of a workpiece is measured using a vibrating sensor.
2. Description of Related Art
There have been known contour measuring instruments that measure a contour such as a profile and roughness of a surface of a workpiece by scanning the surface of the workpiece, the contour measuring instruments including a roughness measuring Instrument, a profile measuring instrument, a roundness measuring instrument and a coordinate measuring instrument.
In such measuring instruments, a vibrating force sensor (hereinafter, abbreviated as a force sensor) 1 as shown in FIG. 10 has been used as a sensor for detecting a surface of a workpiece based on a minute displacement of the contact portion contacting with the surface of the workpiece.
The force sensor 1 shown in FIG. 16 includes a metal base 2, a stylus 3 integrally formed on the base 2, a vibrating element 4 that vibrates (in an axial direction) the stylus 3 and a detecting element 5 that detects a vibration state of the stylus 3 and outputs the vibration state as a detection signal. A contact pin (contact portion) 6 formed of a diamond chip, ruby and the like is fixedly bonded to a tip end of the stylus 3. The vibrating element 4 and the detecting element 5 are formed by a single piece of piezoelectric element, the piezoelectric element fixedly bonded on each of front and back surfaces of the base 2.
As shown in FIG. 11, when a vibration signal Pi (voltage signal) having predetermined frequency and amplitude is applied to the vibrating element 4 of the force sensor 1, the detecting element 5 obtains a detection signal Qo (voltage signal) having predetermined frequency and amplitude.
FIG. 12 shows variation in the amplitude of the detection signal Qo caused by contact with a workpiece W. In a state where the stylus 3 is not in contact with the workpiece W, when the vibration signal Pi having a certain amplitude at a resonance frequency of the stylus 3 is applied to the vibrating element 4, the stylus 3 resonates to provide the detection signal Qo having an amplitude Ao to the detecting element 5. When the stylus 3 comes into contact with the workpiece W, the amplitude of the detection signal Qo attenuates from Ao to Ax.
A relationship between an attenuation rate k (Ax/Ao) and a measuring force is shown in FIG. 13.
Here, description will be given by taking an example of a condition where the detection signal Qo in a contact state of the stylus 3 (force sensor 1) and the workpiece W is attenuated to 90% of a non-contact state (i.e., attenuation rate k=0.9). As seen from the relationship in FIG. 13, the measuring force in the contact state is 135 [μN].
Accordingly, by controlling with an actuator or the like a distance between the force sensor 1 and the workpiece W such that the attenuation rate k is always constant when the force sensor 1 contacts with the workpiece W, a profile and roughness of the workpiece W can be measured with a constant measuring force.
In the contour measuring instrument having the sensor 1 as described above, when the stylus is broken or malfunctioned and unable to make a proper performance, the force sensor 1 needs to be replaced with a new one that can perform properly. In such a case, it is possible to replace a whole unit of the force sensor 1.
However, in the replacement of the whole unit of the force sensor 1, positioning is difficult. When a position after the replacement of the contact pin 6 of the force sensor 1 is displaced from that before the replacement, measuring accuracy might be greatly affected.
With such a background, there has been a demand for an arrangement that can highly reproducibly position the force sensor to the probe.
As an arrangement for positioning a plurality of components with a high reproducibility, a so-called pin-lock method has been known (see, for instance, Document 1: JP-A-10-217004 and Document 2: JP-A-10-J00006).
In the arrangement disclosed in Document 1, an eccentric pin eccentric to the axial core of a crank pin is inserted in a tip attachment hole.
By rotating the crank pin to bring the tip into contact with a lateral wall surface, the crank pin is locked.
In the arrangement disclosed in Document 2, an insert seating section on which an insert is mounted is provided at a tip end of a holder, the insert seating portion provided with a dented pocket that extends through the insert seating section. A root of a pin of a pin member has a tapered surface, and a central hole of the insert is provided with a curved convex surface at a position engaging with the pin.
By fixedly fitting the pin member in the pocket by a fixing bolt and by pressing a hole wall of the central hole of the insert by the pin, the insert is locked on the insert seating portion.
However, in the arrangement of Document 1, since the tip is brought into contact only with the lateral wall surface by the eccentric pin, the tip might be displaced in the axial direction of the eccentric pin.
In the arrangement of Document 2, two components (i.e., the fixing bolt and the pin member) are required for locking the insert, which complicates the arrangement and degrades working efficiency of the locking.